Process for separating off fumaric acid and other minor components during the production of maleic anhydride

A process for decreasing fumaric acid deposits in the preparation of maleic anhydride by heterogeneously catalyzed oxidation of a hydrocarbon selected from the group of benzene, n-butane, n-butene and 1,3-butadiene with molecular oxygen in the presence of a catalyst comprising vanadium, phosphorus and oxygen, comprising

• (a) the absorption of maleic anhydride from the crude product mixture in an absorbent comprising an organic solvent in an absorption column;
• (b) the desorption of the maleic anhydride from the maleic anhydride-enriched absorbent obtained in step (a) in a desorption column;
• and
• (c) the full or partial recycling of the absorbent depleted of maleic anhydride in step (b) to step (a),
• wherein
• (d) the entirety or a portion of the absorbent depleted of maleic anhydride in step (b), for controlled precipitation of fumaric acid, is cooled from a temperature in the range from 100 to 150° C. to a temperature in the range from 30 to 70° C., and/or concentrated by evaporating a portion of the absorbent, to such an extent that the difference between the concentration of fumaric acid in the recycle stream at the outlet of the desorption column c(fumaric acid, desorption column outlet), under the conditions present there, in ppm by weight, and the equilibrium concentration of fumaric acid according to the solubility curve after the cooling and/or evaporation of a portion of the absorbent c(fumaric acid, equilibrium after cooling/evaporation) in ppm by weight, is greater than or equal to 250 ppm by weight and a vessel with internals is used for the precipitation and deposition of the fumaric acid, the mean residence time in the vessel with internals being from 0.05 to 6 hours;
• (e) the fumaric acid precipitated as a solid as a result of the measures from step (d) is removed completely or partly, continuously or batchwise, from the absorbent recycling;
• and
• (f) the fumaric acid-depleted absorbent from step (e) is recycled completely or partly to step (a).